public class Test {
    public static void main(String[] args) {
        People.Heartbeat heartbeat = new People().new Heartbeat();
        heartbeat.show();
    }
}

class People{
    private int heartbeat = 150;
    public class Heartbeat{
        private int heartbeat = 110;
        public void show(){
            int heartbeat = 78;
            System.out.println(heartbeat);//78
            System.out.println(this.heartbeat);//110
            System.out.println(People.this.heartbeat);//150
        }
    }
}
